You can use the Define Users form in the System Administrator responsibility to create new user accounts.
You don't have to create a person before creating a user. However if using HR then doing so lets you link the user to an employee. As Bashar said, unless you are using advanced user security (such as RBAC) then use the Define Users professional form.
Ok thank you.
As a test I will create a user account using the Define Users form in the System Administrator responsibility without create a person before.
And then how can I drop this account ?
I can't remember offhand if you can delete an account or not. If not then you can just end-date it.
Of course don't do this in a production environment anyway though...!